The invention relates to the use of heat-treated bismuth molybdate- and bismuth phosphomolybdate-on-colloidal titania catalysts for the preparation of formaldehyde.
Bismuth molybdate and phosphomolybdate catalysts are known in the art. They have been used for the oxidation of methanol and hydrocarbons, oxidative dehydrogenation of olefins, and also for the oxidation of olefin-ammonia mixtures to unsaturated nitriles.
Bismuth molybdate and phosphomolybdate catalysts are often deposited on a support. In general, silica is disclosed in the art as the preferred support. There are teachings that other materials which are inert may be used as alternate or auxiliary supports. For example, in U.S. Pat. No. 3,186,955, it is disclosed that "A preferred support is silica . . . Many other materials such as alundum, silicon carbide, aluminasilica, alumina, titania and other chemically inert materials may be employed as a support."
Bismuth molybdate and phosphomolybdate-on-silica catalysts may be prepared through use of silica sols, for example, see U.S. Pat. Nos. 3,248,340 and 2,904,580, though, more generally, the supported catalysts are prepared by impregnation of preformed solid inert supports with aqueous solutions of the active catalyst components. Although there are other methods of preparing supported catalysts, to applicants' knowledge, there is no specific description in the art of the preparation of bismuth molybdate-on-colloidal titania catalysts by use of titania sols.
U.S. Pat. No. 3,415,886 discloses calcining colloidal silica supported bismuth molybdate and phosphomolybdate catalysts, of the type described in U.S. Pat. No. 3,248,340 and 2,904,580, at 750.degree.-850.degree. C. to obtain compositions with improved selectivity and directivity in vapor phase oxidations. Further, these treated catalysts that have been heated at 750.degree.-850.degree. C. function, for vapor phase oxidations, at higher temperatures than is the case for the normally calcined product.